Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 300750
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
250 AM CDT SAT APR 30 2016

.SHORT TERM...(Today)
ISSUED AT 249 AM CDT Sat Apr 30 2016

An active weather day is setting up across central and southeast
Illinois for today. A vigorous, but weakening, upper-level low is
slowly approaching the Midwest from the central High Plains. To the
east of this circulation, a tropical moisture plume is surging
toward the area in deep southerly flow. Strong WAA/isentropic ascent
will work on this moisture plume and produce an area of showers with
embedded thunder across the forecast area, primarily this morning.

Rainfall coverage should diminish across the area this afternoon,
with additional development at least partially dictated by how far
north the surface warm front pushes. The afternoon position of this
warm front will help determine how much destabilization can occur
during peak diurnal heating. Model agreement in this regard is still
not great, although the forecast afternoon position of the front has
trended north in the past 24 hours in the latest consensus. The main
severe storm threat this afternoon still appears to be south of I-70
where modest instability (1000-2000 j/kg) and bulk shear (30-35 kts)
appear most likely to co-exist. A large N-S spread in high
temperatures appears likely today given the expected afternoon
position of the warm front. Expect daytime highs to range from the
mid 50s north around Galesburg & Lacon, to around 70 south of I-70.

&&

.LONG TERM...(Tonight through Friday)
ISSUED AT 249 AM CDT Sat Apr 30 2016

Most of the forecast focus will be on the period through Sunday
night, as the current storm system works its way through the region.

Surface low expected to track northeast across the region this
evening, reaching northeast Indiana by midnight, although the GFS is
quite a bit slower with this scenario. General thought is that the
steadier showers will be quickly diminishing by this evening,
with a good portion of the overnight hours dry. However, the
remnants of the upper low currently along the Colorado/Kansas
border will move across southern Iowa Sunday morning and across
Illinois in the afternoon, bringing another period of scattered
showers to the area by midday. Have included isolated thunder
mention in the afternoon most areas, as the trough moves overhead.
Any lingering showers should be out of the area around sunset.

Highly amplified pattern expected next week, as upper level ridging
over the western U.S. builds well into British Columbia and Alberta.
Longer range models showing some differences with the extent of the
corresponding upper trough over the eastern half of the CONUS, with
the ECMWF on the deeper side. This would trend toward significantly
cooler conditions over the Midwest during the second half of the
work week. By the end of the week, the upper pattern on both the GFS
and ECMWF models trends toward an omega block type configuration
which would linger the cooler air even longer. Have trended downward
on the temperatures for late in the week, although not as low as the
blended raw model guidance at this point.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1159 PM CDT Fri Apr 29 2016

VFR ceilings across central IL this evening will deteriorate
overnight from southwest to northeast as a warm front begins to
lift northward toward central IL ahead of a low pressure system
approaching from northeast TX. Consensus of short term model
guidance suggests a deterioration to MVFR by around 09Z at KSPI
ranging to around 12Z at KCMI combined with scattered rain
showers and a chance for some isolated thunderstorms. Further
lowering of ceilings to IFR or locally worse by 14-16Z.
Thunderstorms will become more prevalent and intense after
22Z...especially SE of a KSPI-KBMI line. Decrease in thunderstorm
activity expected after 00-04Z as the low center passes to the
east of the area, with the earliest improvements at KPIA. Ceilings
will struggle to improve much however, especially KPIA-KBMI. Winds
will be from the east-northeast at 10 to 15 kts overnight, then
veer to the east-southeast with gusts to around 25 kts Saturday
morning. Winds decreasing after 00Z.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...BAK
LONG TERM...Geelhart
AVIATION...Onton


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